CI: Run tests against WP 5.7 (#11740)

.github/workflows/tests-e2e.yml

@@ -128,7 +128,7 @@ jobs:
       matrix:
         # TODO: add back Firefox once support is more mature.
         browser: ['chrome']
-        wp: ['5.5']
+        wp: ['5.7']
         snapshots: [false]
         # We want to split up the tests into 2 parts running in parallel.
         shard: ['1/2', '2/2']

.github/workflows/tests-unit-php.yml

@@ -64,7 +64,7 @@ jobs:
             experimental: false
 
           - php: '7.2'
-            wp: '5.5'
+            wp: '5.7'
             experimental: false
 
           - php: '8.0'
@@ -119,15 +119,15 @@ jobs:
       #
       # | WP  / PHP | PHPUnit |
       # |-----------|---------|
-      # | 5.5 / 7.2 | 7       |
+      # | 5.7 / 7.2 | 7       |
       # | 5.9 / 7.2 | 8       |
       # | 5.9 / 7.4 | 9       |
       # | *   / 8   | 9       |
       #
       # See https://make.wordpress.org/core/handbook/references/phpunit-compatibility-and-wordpress-versions/
       - name: Update PHPUnit
         run: |
-          if [[ $WP_VERSION == "5.5" && $PHP_VERSION == "7.2" ]]; then
+          if [[ $WP_VERSION == "5.7" && $PHP_VERSION == "7.2" ]]; then
             echo "Installing PHPUnit 7.5.x"
             composer require --ignore-platform-reqs --no-interaction --no-scripts phpunit/phpunit:^7.5 --with-dependencies
           elif [[ $PHP_VERSION == "7.2" ]]; then